1. Field of the Invention
Diabetes is a general term for disorders in man having excessive urine excretion as in diabetes mellitus and diabetes insipidus. Diabetes mellitus is a metabolic disorder in which the ability to utilize glucose is more or less completely lost. About 2% of all people suffer from diabetes.
Since the introduction of insulin in the 1920's, continuos strides have been made to improve the treatment of diabetes mellitus. To help avoid extreme glycemia levels, diabetic patients often practice multiple injection therapy, whereby insulin is administered with each meal.
In the treatment of diabetes mellitus, many varieties of insulin preparations have been suggested and used, such as regular insulin, Semilente.RTM. insulin, isophane insulin, insulin zinc suspensions, protamine zinc insulin, and Ultralente.RTM. insulin. As diabetic patients are treated with insulin for several decades, there is a major need for safe and life quality improving insulin preparations. Some of the commercial available insulin preparations are characterized by a fast onset of action and other preparations have a relatively slow onset but show a more or less prolonged action. Fast acting insulin preparations are usually solutions of insulin, while retarded acting insulin preparations can be suspensions containing insulin in crystalline and/or amorphous form precipitated by addition of zinc salts alone or by addition of protamine or by a combination of both. In addition, some patients are using preparations having both a fast onset of action and a more prolonged action. Such a preparation may be an insulin solution wherein protamine insulin crystals are suspended. Some patients do themselves prepare the final preparation by mixing an insulin solution with a suspension preparation in the ratio desired by the patient in question.
Normally, insulin preparations are administered by subcutaneous injection. What is important for the patient, is the action profile of the insulin preparation which is the action of insulin on the glucose metabolism as a function of the time from the injection. In this profile, inter alia, the time for the onset, the maximum value and the total duration of action are important. A variety of insulin preparations with different action profiles are desired and requested by the patients. One patient may, on the same day, use insulin preparations with very different action profiles. The action profile requested is, for example, depending on the time of the day and the amount and composition of any meal eaten by the patient.
Equally important, however, is the physical stability of the insulin preparations due to the abundant use of pen-like injection devices such as devices which contain Penfill.RTM. cartridges, in which an insulin preparation is stored until the entire cartridge is erapty. This may last for at least 1 to 2 weeks for devices containing 1.5-3.0 ml cartridges.
2. Description of the Background Art
The first stable neutral insulin suspension was developed by Scott and Fischer (J. Pharmacol. Exp. Ther. 58 (1936), 78) who discovered that the presence of a surplus of protamine and a zinc salt (2 .mu.g zinc per IU (international Unit) insulin) could stabilize the protamine insulin preparation, described by Hagedorn et al.: J.Am.Med.Assn. 106 (1936), 177-180.
Protamine Zinc Insulin made according to the United States or European Pharmacopoeias contains amorphous protamine zinc insulin as well as crystalline Protamine Zinc Insulin. Freshly prepared protamine zinc insulin contains mainly amorphous precipitate which will partly be transformed into crystalline particles upon storage, leading to a more protracted effect.
A completely crystalline protamine zinc insulin modification designated NPH insulin or Isophane Insulin was developed by Krayenbiihl and Rosenberg (see tep. Steno Mem. Hosp. Nord. Insulinlab. 1 (1946), 60; and Danish patent No. 64,708). They found that insulin and protamine brought together in isophane proportions at a neutral pH value in the presence of a small amount of zinc and phenol, or phenol derivatives or, preferably m-cresol, will form an amorphous precipitate which upon standing is gradually but completely transformed into oblong tetragonal crystals limited at the ends by pyramidal faces. Insulin and salmon protamine co-crystallize in a weight ratio corresponding to about 0.09 mg protamine sulphate per mg insulin. Zinc in an amount of at least 0.15 .mu.g per IU and a phenolic in a concentration higher than 0.1% is necessary for the preparation of the tetragonal crystals.
In the early days, this kind of crystals were prepared using, porcine and bovine insulin from natural sources, but from the eighties also human insulin, made by genetic engineering or by semisynthesis, is used.
Human insulin consists of two polypeptide chains, the so-called A and B chains which contain 21 and 30 amino acids, respectively. The A and B chains are interconnected by two cystine disulphide bridges. Insulin from most other species has a similar construction, but may not contain the same amino acids at the positions corresponding in the chains as in human insulin.
The development of the process known as genetic engineering has made it possible easily to prepare a great variety of insulin compounds being analogous to human insulin. In these insulin analogues, one or more of the amino acids have been substituted with other amino acids which can be coded for by the nucleotide sequences. As human insulin, as explained above, contains 51 amino acid residues, it is obvious that a large number of insulin analogues is possible and, in fact, a great variety of analogues with interesting properties have been prepared. In human insulin solutions with a concentration of interest for injection preparations, the insulin molecule is present in associated form as a hexamer (Brange et al. Diabetes Care 13, (1990), 923-954). After subcutaneous injection, it is believed that the rate of absorption by the blood stream is dependent of the size of the molecule, and it has been found that insulin analogues with amino acid substitutions which counteract or inhibit this hexamer formation have an unusual fast onset of action (Brange et al.: Ibid). This is of great therapeutic value for the diabetic patient. In the crystals of the prolonged acting protamine insulin preparations, the insulin is also found to be hexameric (Balschmidt et al.: Acta Chryst. B47, (1991), 975-986).
Pharmaceutical preparations which are based on analogues of human insulin are e.g. known from the following documents:
WO 95/00550 is concerned with pharmaceutical preparations based on insulin crystals comprising Asp.sup.B28 insulin and protamine, which display rapid onset and prolonged activity when administered in vivo. The crystals may furthermore contains zinc ions and phenol and/or m-cresol. Glycerol is added to the preparations as isotonicity agent.
In U.S. Pat. No. 5,461,031 various parenteral pharmaceutical formulations, which comprise a rapid-acting monomeric insulin analogue, zinc, protamine and a phenolic derivative, is disclosed. The formulations furthermore contain glycerol which acts as an isotonicity agent.
U.S. Pat. No. 5,474,978 discloses a rapid acting parenteral formulation comprising a human insulin analogue hexamer complex consisting of six monomeric insulin analogues, zinc ions and at least three molecules of a phenolic derivative. The preferred isotonicity agent is glycerol.
Unfortunately, insulin tends to form insoluble and biologically inactive fibrils by non-covalent polymerization (c.f. e.g. Jens Brange, Galenics of Insulin, Springer-Verlag, 1987 and references therein). Fibril formation is promoted by elevated temperatures, e.g. above 30.degree. C., and concomitant movements. This fibrillation process, which is very difficult to avoid, poses an upper limit on the period for which the insulin preparation can be stored and, hence, on the cartridge volume of Penfills.RTM..
Since the formation of fibrils generally requires a monomerization of insulin, insulin analogues which more reluctantly form di- and hexamers, result in preparations of less physical stability due to fibrillation.
Thus, it is an object of the present invention to provide an insulin preparation comprising human insulin or an analogue or derivative thereof with improved physical stability.
According to the invention this object has been accomplished by an aqueous insulin preparation comprising dissolved and/or precipitated human insulin or an analogue or derivative thereof, and a water-soluble reduced or non-reducing carbohydrate containing at least 4 carbon atoms in the main carbohydrate structure, or a water-soluble non-reducing ester and/or ether derivative of a carbohydrate or reduced carbohydrate containing at least 4 carbon atoms in the main carbohydrate structure, or mixtures thereof.